1. Field
This disclosure relates generally to the field of dimming control of light fixtures. More particularly, the disclosure relates to high-end trim adjustment in a dimming controller for light-emitting diode (LED) based light fixtures.
2. Related Art
Light sources may be controlled by a light switch or a dimmer control. A light switch is used to turn a light source on or off. A dimmer control is used to reduce the light emitted by a light source, thereby setting the ambient light intensity to be somewhere between that experienced when the light source is off and that experienced when the light source produces light at full intensity.
Some dimming controls cause drivers to power light emitting diodes (LEDs) at a light intensity that depends on the voltage of a lighting control signal. In some lighting systems, potentiometers are used as a dimmer to set the intensity of the light fixture when it is on.
FIG. 1 illustrates a lighting fixture 102 that is powered through a power line 180 by a power source 101. The lighting fixture 102 includes a light emitting diode (LED) driver 110 that is controlled by a potentiometer 100 and drives an LED array 120. The LED driver 110 receives a 0-10 volt lighting control signal through a control channel 160.
The LED driver 110 drives a current from an internal 10V reference (not shown) through an internal pull-up resistor (not shown) into one terminal of the control channel 160 to the potentiometer 100. The potentiometer 100 has a variable resistance. The potentiometer 100 causes the voltage across the control channel 160 to be between 0 and 10 volts depending on the variable resistance of the potentiometer 100 relative to the resistance of the internal pull-up resistor.
The LED driver 110 drives onto a controlled power line 170 a current that depends on the voltage of the lighting control signal on the control channel 160. The controlled power line 170 powers the LED array 120. The LED array 120 includes one or more LED devices configured to be powered by the controlled power line 170. The light intensity produced by the LED array 120 depends on the lighting control signal.